The present invention relates to a method of and an apparatus for controlling injection of a fuel into an internal combustion engine. More particularly, the invention is concerned with a fuel injection controlling method and apparatus in which the rate of synchronous injection is increased and/or asynchronous injection is conducted in response to a change in the intake pressure of the engine.
Modern internal combustion engines are equipped with an electronic fuel injection controller which is adapted to effect a synchronous fuel injection in synchronism with stroking of pistons, i.e. at every predetermined crank angle, at a rate which is computed on the basis of the load on the engine and the engine speed. In this type of engine, the electronic fuel injection controller has a function of effecting an acceleration incremental correction in which the rate of synchronous fuel injection is increased when the engine acceleration demand is higher than a predetermined level and also a function to effect an asychronous fuel incremental injection in which the fuel injection rate is increased regardless of the crank angle when the engine acceleration demand is higher than the predetermined level.
In some engines of the type described, the pressure of intake air in the intake pipe of the engine is used as the index of the engine acceleration demand so that the acceleration incremental correction and the asynchronous incremental injection are effected when the amount of change in the intake pressure is higher than a predetermined reference level. In these engines, the reference level is maintained constant regardless of the level of the load applied to the engine. In addition, this reference level is selected to be rather small, in order that the acceleration incremental correction and the asynchronous incremental injection may easily be carried out even when the load applied to the engine is comparatively low.
This known fuel injection control encounters the following problem. Namely, in the full-load operation of the engine, a large pulsation of intake pressure takes place in the intake pipe. It is, therefore, often experienced that the reference level of the intake pressure change is exceeded by the amplitude of pulsation of the intake pressure so that the acceleration incremental correction or the asynchronous incremental injection are put into effect undesirably even though there is no substantial demand for engine acceleration. In such a case, the air-fuel mixture is rendered excessively rich adversely affecting the performance of the engine and the exhaust emissions, as well as the fuel consumption.